The "what if the power goes down" argument is probably the lamest one in the book.

In that case, yes, Bitcoin will be useless.

So will gold.

So will Tesla stocks.

So will money in the bank.

The only things of value will be food, water, and guns.

BUT - when the power comes back on - and it eventually will - you will have the exact same amount of sats you had before it went out.